The conventional approach to assembling components on both sides of a double sided printed circuit board (PCB), using a reflow soldering process, consists of applying solder paste screen on one side of the PCB, placement of the components on the solder paste and soldering of the components in the reflow oven. This process is repeated on the second side of the PCB. The solder paste screen printing (cladding) is the most difficult and critical stage with regard to the reliability of the soldering process. Some techniques, that are in use to avoid this cladding stage, provide flat solid solder deposit and are carried out by the printed circuit board manufacturer. The process at an assembly plant consists of flux dispensing on the cladded pads, placement of the components on the flux, soldering of the components in the reflow oven, followed by a repetition of all the above process stages on the second side of the PCB. During the first reflow the cladding of the second side of the PCB changes its flat shape to a meniscus form, thus resulting in slippage of the components from the pads and faulty soldering of components.
Thus, there exists a need for an improved soldering process that prevents a meniscus formation of the solder paste during reflow operations, in particular with regard to the cladding of double sided PCBs.